You are given a table, Functions, containing two columns: X and Y.

Two pairs (X₁, Y₁) and (X₂, Y₂) are said to be symmetric pairs if X₁ = Y₂ and X₂ = Y₁.

Write a query to output all such symmetric pairs in ascending order by the value of X. List the rows such that X₁ ≤ Y₁.

Sample Input

Sample Output

20 20
20 21
22 23